Stormy then cold blast for the new year?

December has been a mild month overall, and Christmas was green across the UK. However, a significant change is forecast as we approach the new year. Heavy rain, stormy conditions, and snow all pose a risk of disruption.

Stormy around New Year's Day?

Computer models indicate the risk of very windy conditions around the turn of the year, but there are significant differences in their predictions at present. These differences stem from the track and intensity of areas of low pressure expected to move in from the Atlantic.

The strongest winds are likely to occur on the southern and western flanks of the low pressure systems. Colder air wrapping around them could lead to snow on their northern and western edges as they move eastwards.

Most computer models show the first low pressure system tracking across the north on New Year's Eve. However, there is still some uncertainty, with a few models suggesting a more southerly route. The strongest winds currently appear most likely to affect northern and western areas, with snow mainly in Scotland.

The chart above, from the UKV model, shows forecast gusts at midday on New Year's Eve. As details are still uncertain, it is included for illustrative purposes only. If you are planning to head out be sure to stay updated with short range forecasts and weather warnings issued by the UK Met Office.

Met Office Global pressure and precipitation

The second low pressure system is expected to track farther south. Consequently, the strongest winds are likely to impact the southern half of the UK. Additionally, the boundary between cold and mild air masses is forecast to lie somewhere over the southern half of the UK. Significant snowfall could occur near this boundary. Past experience indicates that the specifics of such events often remain unclear until about a day before they are expected to happen.

As a result, disruption due to the weather is likely in parts of the UK between 31st December and 2nd January. Wind gusts of 40 mph to 75 mph are possible across large areas. While the snow risk remains highly uncertain, some locations could experience substantial snowfall.

Cold spell follows the storms?

As the low pressure areas move away eastwards, much colder Arctic air is forecast to sweep southwards. Initially high pressure will be centered over the Atlantic, but it is likely to gradually edge eastwards. The general pattern suggests that sleet and snow showers will be most likely in northern and eastern Britain. December has been frost free in some locations, but early January could bring very cold nights, offering a stark contrast.

The data table above shows the temperature forecasts for London for the next 16 days. Between 2nd and 12th January the majority of runs in the model are forecasting maximum temperatures to be either cold or very cold.

The positioning of the high pressure will significantly impact how the cold spell develops. If the high pressure shifts eastwards, much milder air could would gradually move in from the southwest. Alternatively, if it migrates northwards, a prolonged and potentially severe cold period is likely to follow.

At this stage, it is not possible to discuss the snow risk in anything but general terms. If the high pressure becomes centered farther north, the likelihood of snow would increase: either in the form of showers or more widespread outbreaks, potentially occurring as milder air attempts to return.

Recent climatology provides a note of caution

January 2023 brought a cold spell; however, it ended 0.9°C milder than the 1961–1990 Central England Temperature (CET) average and exactly in line with the milder 1991–2020 series. Cold months have been rare in recent years, so the likelihood of January and February turning out to be cold is statistically low. Additionally, long range computer models have consistently indicated a mild pattern dominating northwestern Europe for much of the winter.

Therefore, despite some medium-range computer models suggesting a lengthy cold period, a mixed January remains favoured at this point. The last January to be colder than the 1961–1990 average was in 2021, before that it was 2013, cold Januaries have been scarce in recent years.

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